1. Field of the Invention
This invention relates to lubricating oil compositions which exhibit marked improvement in the detergency characteristics resulting in lower engine carbon deposits and makes available an internal combustion engine oil package, both for gasoline and diesel engines, with substantial improvement in the biodegradability. More particularly, this invention is directed to lubricating oil compositions for internal combustion engines which contain a synergistic mixture of calcium phenate overbased detergent which is derived from cashew nut shell liquid (CNSL) and an amine salt of phosphorodithioic acid derived from CNSL.
2. Background of the Related Art
Lubricant additives can be classified as materials that impart new properties to or enhance existing properties of the lubricant into which these are incorporated. The lubricant additives, besides showing enhanced performance, need to be cost-effective, easily manufactured and should have higher biodegradability.
Detergents, anti-wear and antioxidants constitute a major class of lubricant additives, which find application in engine lubricants especially for internal combustion gasoline and diesel engines. Among the conventionally used detergents in lubricating oil additives are metallic sulfonates, phenates and salicylates. Metallic phenates and sulfurized metal phenates are one of the widely used detergents in lubricating oils, for mainly internal combustion gasoline and diesel engines, and these function to neutralize acid substances, sludge etc., generated in an engine. Thus, the metallic phenates, generally alkaline earth metal phenates, provide engine parts with good protection from excessive corroding caused by acidic substances and prevent excessive wear caused by sludge. The overbasing of these phenates helps in fighting the acids produced during the combustion of fuel, while the sulfurization mainly helps to improve heat stability.
The conventional method of making overbased metallic sulfurized phenates, useful as lubricating oil additives, involves reacting alkyl substituted phenols, generally para-substituted, with sulfur, metal salts followed by carbonation. Thus, U.S. Pat. No. 2,370,302 discloses the use of sulfurized phenates in lubricating compositions which are subjected to higher temperatures. Similarly, U.S. Pat. No. 3,367,867 discloses the use of sulfurized overbased calcium phenates as detergents in lubricating oils for internal combustion engines. U.S. Pat. No. 4,874,007 discloses a process for preparation of sulfurized alkyl-substituted phenates to be used as detergents. In U.S. Pat. No. 5,910,468, we have already described a process for the preparation of calcium phenate detergents derived from naturally occurring and biodegradable cashew nut shell liquid. It was surprisingly discovered that overbased calcium phenates derived from cashew nut shell liquid had low viscosity at high basicity, good oil solubility and higher biodegradability. These phenates could be prepared in an economically advantageous manner and showed remarkably good detergency.
The anti-wear protection and protection against oxidation at high temperature to a lubricating oil used in internal combustion engines is generally met by addition of metallic dialkyldithiophosphates. However, these metallic dithiophosphates contribute to the total ash content of the lubricant composition. Since the zinc is a source of sulfated ash and phosphorus is a poison for catalytic converters, the art has sought to reduce both Zn and P from the lubricating oil compositions (see U.S. Pat. Nos. 4,147,640; 4,330,420; and 4,639,324). While the prior art has been successful in reducing the zinc additive, giving a low ash lubricant formulation, the total removal of zinc has not been recommended as a practical proposition. U.S. Pat. No. 4,330,420 discloses the inclusion of synergistic amounts of dialkyldiphenyl amine antioxidant and sulfurized polyolefins to bring down the amount of zinc dithiophosphate. U.S. Pat. No. 4,089,791 relates to a low ash mineral lubricating oil composition comprising zinc dialkyldithiophosphate, overbased alkaline earth metal salts and a trialkanolamine compound as an additional anti-oxidant component to compensate for the reduced ZDDP. In U.S. Pat. No. 5,916,850 and EP Pat. No. 0915097A1, we have disclosed a process for the preparation of various amine salts of phosphorodithioic acids, derived from cashew nut shell liquid, which, when blended into lubricants, provide effective anti-wear, anti-oxidant and friction reducing properties. Inclusion of these ashless dialkyldithiophosphates into the lubricant formulations for internal combustion gasoline and diesel engines, has resulted in reduction of ash content. These dialkyldithiophosphates, surprisingly, have shown a synergistic boost to the detergency action of CNSL derived sulfurized metallic phenate additives.
An object of this invention is to propose a synergistic composition of lubricating oil for internal combustion gasoline and diesel engines, which exhibit higher detergency and lower ash content. Another object of this invention is to disclose synergistic lubricating oil compositions for internal combustion engines containing sulfurized overbased calcium phenates derived from cashew nut shell liquid and multifunctional additive based on amine salts of phosphorodithioic acids derived from cashew nut shell liquid resulting in higher oxidation stability, higher detergency, lower zinc and phosphorus content and higher biodegradability.
A lubricating oil composition for gasoline and diesel internal combustion engines includes a major portion of an oil of lubricating viscosity; from 0.1 to 20.0% w/w of a component A which is a sulfurized, overbased calcium phenate detergent derived from distilled, hydrogenated cashew nut shell liquid; and from 0.1 to 10.0% w/w of a component B which is an amine salt of phosphorodithioic acid derived from cashew nut shell liquid and has a general formula as follows: 